Lessons Learned Every Year

For six years, Quincy, Mich., farmer Leon Knirk has varied plant populations by zone to maximize production.

"I’ve got my foot on the gas and am pushing to get as much as I can out of every single acre. I want bushels, and I need bushels. But I want to be precise with my inputs," he says. "With variable-rate populations, it might not always lead to more bushels, but in those years it could be the same bushels with 2,000 less plants."

Knirk says he sees the benefits of variable-rate population go both ways. On the journey, he’s trying to learn something every year.

It was a new planter outfitted with hydraulic drive and rate controller that convinced him to head to the field with variable-rate populations. Before that, he changed populations between fields based on the overall soils.

He uses software to develop most of his variable-rate population maps, along with working with his agronomist, Farm Journal Associate Field Agronomist Missy Bauer. In doing the analysis of the results, he says it’s putting it all together by breaking your fields apart by management zone.

"I do complete field analysis as well as by hybrid," he says. "We do check strips here and there. Then I look back at all the numbers and see where did we excel and where we didn’t. I like to see that as my population goes up, my yield goes up. If something has changed or we didn’t see the progress, then now we have to look at something else."

In-season ground-truthing and remote sensing help color in the yield analysis picture.

"We walk a lot of fields doing ear evaluations and use NDVI maps as additional layers," Knirk says. "We want to use our knowledge to produce the most we can out of this ground. On our irrigated acres, we’re still pushing populations."

Hybrid response to populations is another aspect of variable-rate population where Knirk says there is more to learn. "In the past, we could have used the prescriptions year after year with success, but now we are getting more hybrid specific. We’ve figured out we’re doing a better job with hybrid placement. We can alter our variable-rate populations based on information from the seed companies," he says.

With all of the knowledge applied, Knirk says his confidence in the agronomic decisions he makes has grown.

"When we started using variable-rate populations along with variable-rate nitrogen, I could tell that we were applying inputs where they belonged. Our numbers showed it," he says. "I can look at my seed costs and other inputs, and I can get more production out of the same dollars."